Choir fiddled about with a man’s organ (9)
I believe the answer is:
harmonica
'organ' is the definition.
(I've seen this before)
'choir fiddled about with a man's' is the wordplay.
I cannot quite understand how this works, but
'about' could be 'on' (as in a book 'on' a certain topic) and 'on' is found in the answer.
'a' is present in the answer.
'man' could be 'mic' and 'mic' is found in the remaining letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for harmonica that I've seen before include "Mouth organ" , "glasses of water" , "Larry Adler's instrument" , "Blow me!" , "Small wind instrument" .)